All the books say to tell people when you stop smoking
Just because all the books say it, doesn't necessarily make it a good idea. There are three major confounding factors in self-help literature:
People repeat ideas that sound good
Some procedures are shibboleths or survivor-bias filters. That is, if you're willing to tell people you've quit, it's likely correlated with your actual judgment of your ability to do so. Thus, the procedure gets credit for success, and the person who can't bring themselves to do it gets the blame for failure.
There are at least two major divisions of people who respond differently to self-help advice; the ones I dub "naturally struggling" and "naturally successful". Techniques aimed at the latter can actually do more harm than good when used by the former... and there's now research that shows positive thinking can actually hurt your outlook -- a result I've previously predicted in my writings.
I consider any setup that encourages a naturally struggling person to compare their behavior against an ideal, with negative consequences for deviation, to be the equivalent of prescribing bar time as a cure for alcoholism!
A naturally struggling person already compares their behavior to ideals of perfection, and beats themselves up internally for every minor deviation. They need less of that, not more.
Here's the kind of advice I mean:
"Tell people that you're trying to quit. Don't hide your attempt because you're afraid people will see you fail. Most people know how hard it is to quit smoking and that many smokers have to try several times before they succeed. Support can help you quit smoking, and experts recommend getting support from friends, family, and coworkers."
It is true that ideas that sound good get passed around - but also ideas that are counter-intuitive and ...
A blog post by Derek Sivers links to evidence that stating one's goals makes one less likely to accomplish them.
Excerpt:
Link: Shut up! Announcing your plans makes you less motivated to accomplish them.